As the sun dips below the horizon and the light starts to dim, lucky observers may spot a rare, brief flash of emerald. This is the “green flash,” which can sometimes be seen right after sunset or before sunrise.
So what causes the green flash?
Like many colorful spectacles in the sky, such as rainbows, the green flash is the result of sunlight being separated into different colors. Normally, sunlight is white because it is made up of all of the wavelengths of visible light, Johannes Courtial, an optics researcher at the University of Glasgow, told Live Science. But when white light passes through a medium that is higher-density, like glass or water, at an angle, wavelengths of different colors start to bend and separate. This separation is called refraction.
Earth’s atmosphere, with its varying density of gases, can refract light, too. It’s why we sometimes see rainbow halos around the sun, or mirages in the distance, said Jan…
